Provision of compact and inexpensive sensors for determination of movement of an object has been pursued for some time.
In Detection of movement with laser speckle patterns: statistical properties, Schnell et al., Vol. 15, No. 1, January 1998, J. Opt. Soc. Am., a sensor for determination of in-plane movement of a diffusing object is disclosed. The object is illuminated with coherent light and a speckle pattern is formed by interaction of the light with the surface of the object. Two interlaced differential comb photo detector arrays act as a periodic filter to the spatial-frequency spectrum of the speckle pattern intensity. The detector produces a zero-offset, periodic output signal versus displacement that permits measurement of the movement at arbitrarily low speed. The direction of the movement can be detected with a quadrature signal produced by a second pair of interlaced comb photo detector arrays.
In WO 98/53271, a sensor for determination of angular displacement of one or more parts of an object is disclosed. The determination is also based on speckle patterns and is independent of the distance to the object, any longitudinal and transversal movements, the shape of the object, and the radius of angular displacement.
In T. Ushizaka, Y. Aizu, and T. Asakura: “Measurements of Velocity Using a Lenticular Grating”, Appl. Phys. B 39, 97–106 (1986), and Y. Aizu: “Principles and Development of spatial Filtering Velocimetry”, Appl. Phys. B 43, 209–224 (1987), discloses utilization of a so-called lenticular grating for deflection of light scattered from a particle onto photo detectors. A particle traversing a measurement volume is illuminated by diffuse light from a He-Ne laser (5 mW) illuminating a ground glass placed at the measurement volume. It is a fundamental characteristic of the measurement system disclosed that the moving particle is imaged onto the lenticular grating. Thus, the distance between the lenticular grating and the moving particle has to be accurately controlled. Furthermore, a set of lenses is placed behind the lens array in order to adequately collect light onto the detectors. This eliminates the possibility for realizing a compact one-element optical system.